Berkeley lab scientists generate low-cost, hybrid thermoelectrics

November 8, 2010
by Aditi Risbud

Using simple water-based chemistry to wrap a polymer that conducts electricity around a nanorod of tellurium, this composite nanoscale thermoelectric is easily spin cast or printed into a film.

Although climate-controlled car seats don't spring to mind when you think of energy efficiency, the latest technology underpinning this luxury automobile feature is based on thermoelectricsmaterials that convert electricity directly into heating or cooling. Conversely, thermoelectrics can also funnel excess heat from energy inefficient systems, such as car engines or power plants, by recovering this 'waste heat' and turning it into electricity. As a result, these materials offer a potentially clean source of energy to reduce fuel consumption and CO2 emissions.

Currently, this thermal energy is converted with high-efficiency, expensive thermoelectric materials. In automotive exhaust systems, for example, solid-state thermoelectrics recover waste heat that can result in fuel savings of up to five percent, but their high cost bars them from being used in smaller-scale settings. Boosting these savings through lower-cost materials could make a significant impact in power generation for batteries or electronic components in computers.

Now, Lawrence Berkeley National Laboratory (Berkeley Lab) scientists are tackling this challenge by changing the budget for thermal energy management, said Jeff Urban, Deputy Director of the Inorganic Nanostructures Facility at the Molecular Foundry, a nanoscience user facility.

Historically, high-efficiency thermoelectrics have required high-cost, materials-intensive processing, said Urban. By engineering a hybrid of soft and hard materials using straightforward flask chemistry in water, weve developed a route that provides respectable efficiency with a low cost to production.

In their approach, Urban and colleagues constructed a nanoscale composite material by wrapping a polymer that conducts electricity around a nanorod of telluriuma metal coupled with cadmium in todays most cost-effective solar cells. This composite material is easily spin cast or printed into a film from a water-based solution. Along with its ease of manufacture, this hybrid material also has a thermoelectric figure of merit thousands of times greater than either the polymer or nanorod alonea crucial factor in boosting device performance.

In recent years, weve seen tremendous gains in thermoelectric efficiency, but there is a need for low-cost, moderate efficiency materials that are easy to process and pattern over large areas, said Rachel Segalman, a faculty scientist at Berkeley Lab and professor of Chemical and Biomolecular Engineering at University of California, Berkeley. We had a lot of intuition about what would work using polymers and nanocrystals, and will now explore materials space to optimize these systems and switch to more earth-abundant materials.

More information:
A paper reporting this research titled, Water-processable polymer-nanocrystal hybrids for thermoelectrics, appears in Nano Letters and is available to subscribers online. Co-authoring the paper with Urban and Segalman were Kevin See, Joseph Feser, Cynthia Chen and Arun Majumdar.

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4 comments

Lots of problems still to overcome here, but when someone finally comes up with the silver bullet of thermoelectric designs, it'll be a world changer. If they can get a material that meets the parameters needed to work in things like building air conditioners, computers, televisions, refridgerators, and water heaters, even a moderate energy efficiency boost would have profound effects on the global economy and energy use. The problem for researchers is that there's HUGE money at stake here, and it's a race to be first to market. Then, when someone makes it to market with a good product, they have to stay on top of the market long enough to turn a profit. There are many organizations trying to solve this problem right now, due to the amazing potential. A good thermoelectric design would have more impact than cost-effective solar energy, so it's a BIG deal.

Sure would be sweet to see someone come up with a $10,000 10 kwe thermoelectric system which could convert 25% of a burner's energy output to electricity. Home heating, hot water heating would be revolutionized (if the grid owners would let us connect it, fat chance).

There are places where the grid owners wouldn't have a say in it. The bread factory where I work has a gas oven over 20 feet tall and more than 100 feet long that runs at about 450 degrees pretty much around the clock. Then there's another oven that's slightly smaller on the other line. If we could cost effectively recycle our waste heat it would be a big deal. Our utilities bills are a huge portion of our production costs.

This idea is anything else but new. In general the idea would be a big deal, but the author himself mentioned some critical issues:efficient and low-costs thermoelectric materials that are easy to process and pattern over large areas...As long these problems are not solved this is pure fiction, but a fiction that is worth to think about and to work on it to become reality.

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